IC Engine Performance Parameters
The primary function of an internal combustion engine is to transform heat energy into mechanical energy. In practical terms, this means that any type of IC engine generates mechanical work in the form of a rotating shaft, delivering torque at specific RPMs through the continuous combustion of fuel. The performance of an IC engine refers to how effectively it accomplishes this task. Evaluating or comparing engine performance is possible only through specific parameters outlined in this chapter, which are commonly referred to as performance parameters.
Indicated Power (IP)
Indicated Power (IP) refers to the overall power generated through the combustion of fuel within the combustion chamber.
Brake Power (BP)
Brake Power refers to the power output available at the engine's output shaft. It represents the power that can be effectively utilised to overcome resistance or counteract the braking forces in the specific application where the engine is employed.
Frictional power
The Friction Power of an engine is the power needed to overcome internal friction within the engine. It accounts for the total losses incurred from the indicated power, and it is the difference between the indicated power and the brake power.
Mechanical efficiency
The Mechanical Efficiency of an IC Engine is the ratio of the brake power to the indicated power.
Indicated Mean Effective Pressure
Mean Effective Pressure (MEP) is the theoretical pressure assumed to be exerted on the piston during the power stroke of an engine. It represents the average pressure that would produce the same amount of work as the actual mechanical work generated per engine cycle.
Brake mean efficiency pressure
Similar to the Indicated Mean Effective Pressure (IMEP) that is based on indicated power, the Brake Mean Effective Pressure (BMEP) is a hypothetical average pressure acting on the piston. BMEP is derived from the brake power of the engine, providing an estimation of the mean effective pressure that would produce the same amount of work as the actual brake power.
Specific output
Specific Power is a performance parameter defined as the brake power output per unit of piston displacement. It serves as a measure of the power-to-size ratio of an engine, making it a significant indicator of engine performance.
Volumetric efficiency
Volumetric Efficiency of an IC Engine is the ratio of the actual volume of the air or charge drawn into the cylinder during the suction stroke (adjusted to standard conditions) to the swept volume of the piston. It quantifies the effectiveness of an engine in utilising its maximum cylinder capacity for intake and is an important factor in evaluating engine performance.
Specific fuel consumption
Specific Fuel Consumption is the measure of the fuel consumption rate of an engine, expressed as the mass of fuel consumed in kilograms per hour per kilowatt (kW) of power produced. It provides insight into the efficiency of an engine in converting fuel into mechanical power output.
Thermal efficiency
Thermal Efficiency is the ratio of work done or power developed by an engine to the rate of chemical energy or heat supplied by the combustion of fuel in the engine. It quantifies the efficiency of an engine in converting the heat energy from fuel combustion into useful mechanical work.
Compression Ratio
The Compression ratio of an IC Engine is the ratio of the total volume of the combustion chamber with the piston at the bottom dead Center (BDC) position to the volume of the chamber when the piston is at the Top Dead Center (TDC) position. Its higher value represents an improvement in the engine efficiency and power output,
Air-to-Fuel Ratio
The air-to-fuel ratio (AFR) refers to the ratio of the mass of air to the mass of fuel in a combustion process. It plays a critical role in the combustion efficiency and performance of internal combustion engines. Here are some key points about the air-to-fuel ratio:
This ratio is typically expressed in terms of mass and connotes the ideal ratio at which all the fuel is completely combusted with the available oxygen. For gasoline, the stoichiometric ratio is approximately 14.7:1, meaning 14.7 parts of air to 1 part of fuel by mass. A lean air-to-fuel ratio refers to a fuel-lean mixture with more air relative to the available fuel. It is expressed as a higher value than the stoichiometric ratio, such as 16:1.
Cylinder Pressure in IC Engine
Cylinder pressure refers to the pressure exerted by the combustion process within the cylinders of an internal combustion engine. It is a key parameter that influences engine performance and efficiency. Cylinder pressure is the result of the combustion process that occurs when the fuel-air mixture ignites within the combustion chamber. The pressure within the cylinder increases rapidly during the combustion phase, reaching its peak value known as peak cylinder pressure (PCP) or peak firing pressure. Cylinder pressure is typically measured using pressure sensors or transducers installed within the combustion chamber or in the cylinder head.
Also, get an insight into Torsion of Circular Shafts.
